我会守护沧海变桑田
[wŏ huì shŏu hù cāng hăi biàn sāng tián]
It translates as 'I will protect until the sea turns into farmland' which references a very ancient saying illustrating an enormous change occurring over extremely long periods. Metaphorically speaking, it expresses a resolve so unwavering, it lasts through great changes and timescales, highlighting devotion.